In the "everything I know is wrong" category, I'm pleasantly surprised at how well my alleged 91db speakers work with my HO (12 watts or maybe 17 watts…jury is out on output)…I listen to a wide range of music including modern jazz, orchestral stuff, things that rock, etc., and my listening space is around 18 by 20 with the ceiling going from maybe 8 to 20 feet sloping up from the gear heap. My main speakers are maybe 8 feet or so from my earballs and can be enjoyed to seriously loud levels with no apparent distortion…easy to see where that distortion shows up by simply turning it up until it goes into overload, but it's loud enough to not have to go near that area. 2 subs reinforce things, but dynamic classical and everything else doesn't seem challenged at all…I might be lucky.

I don't think Dennis has built very many 17wpc Inspires. I think I've only seen one of them for sale on eBay. This design pushes the standard KT88 tubes pretty hard and may not be his preferred model in terms of producing a sweet SE sound.

If I'm not mistaken the lam stack on the OPTs is significantly thicker on the 17w units. The standard having adout 1" thickness and the higher watt units being closer to 2". I top view picture should tell the tale.

What is the lam stack? This is what my amp looks like:

Regardless of the capability of the OPT, I'm not convinced driving the snot out of the output tubes gives the best sound. I own a [15 watt opt] KT88HO and a PSE. In both cases I find my best sound is with tube combinations that give less power than I could get by going with the 5AR4/KT88 combination. In my system and to my ears I find my KT88HO sounds best with a 5U4/6V6GT combination and my PSE sounds best with KT77'. Neither combination was chosen to give more power.

My opinion is that if you need the extra power you get going from a 12wpc KT88 to a 17wpc KT88 amp you really need to step up to the PSE. That being said, the larger OPT's on the 17wpc amp may provide better bass response even at lower power, though there may be a tradeoff. I have not listened to a 17wpc amp so cannot offer my direct opinion.

Does anyone know for a fact if these amps can be bridged to mono without detriment to the sound quality? If so, can a single preamp (Lp-27a) feed both monoblocks by bridging the selector for the two pairs of outputs (to avoid splitting a single output pair's signal)?

The lam stack is where DH puts his Inspire label. At the angle of the photo it looks like you have the higher watt version but it is hard to see clearly. Attachment 51535

These are the 15W opts.

Yeah looks like I have the higher watt version:

I am not certain if having the 20W output transformers is a guarantee that one has the 17 wpc version. It depends upon the voltages in the circuit. Perhaps Dennis always used the 15W OTs with the 12 wpc designs?

As to driving the tubes hard, Dennis has previously stated that he feels the amps sound better when they are not driven to maximum. When he released the PSE amps, he said that they would produce something like 22-24 watts with two KT88s per channel, not overdriving them because he felt this was where they sounded best.

I purchased the 17 watt version, used, for a price below the 12 watt new. I felt I needed every watt I could get as even with my SS amp - spec'ed at 180wpc with dual external power supplies and which has been measured to get to 260 before clipping - I have clipped it a few times.

Going to a PSE would buy me what, 1 more decibel? But then maybe more magic in every watt.

I am content with using my Inspire for moderate volume levels, which is where I listen the vast majority of the time. The SS amp is there for when I want to crank it up.

Would I love a 60wpc tube amp with the magical sound of an Inspire? Sure! But I have no idea if such an amp exists. Right now I am pondering the purchase of a pair of 450wpc monoblocks! Not because I need 450, but because they would provide essentially limitless clean power and there is something to be said about having even the most fleeting transient reproduced with no strain.

Agreed. In my case, only an SS amp would give me the extra "oomph" I need for some classical music selections. The rest can be played at excellent SPLs with extraordinary sound quality through the Inspire HO / LP-27a combo, and even with the amp by itself along with the balanced-fed ZBit (great sound!). Therefore, IMO a PSE would not add much to the equation. Assuming it is feasible, bridging the Inspire amp and buying another unit would probably not be enough either.

The only other possibility is to find an affordable 110+ dB/W/M pair of speakers ... a much more difficult proposition!